In general, protective films are formed on the surface of color filters in liquid crystal displays (LCDs) for the purpose of planarizing and protecting the color filters. Ideally, such surface-protective films should have the desirable optical transparency and also possess sufficient film strength. In addition, such surface-protective films should have sufficient heat resistance to withstand subsequent processes for forming transparent conductive films on the protective films. Further, in some LCDs, such as vertical-alignment LCDs, it is also desirable that the surface-protective films possess sufficient acid resistance to withstand etching and sufficient base resistance to withstand resist peeling.
Materials and methods for forming protective films for color filters are known in the art. For example, Japanese Patent Laid-Open No. Hei 1-134306 describes the use of glycidyl methacrylate as a main component in a protective film, Japanese Patent Laid-Open No. Sho 62-163016 describes the use of a polyimide as a main component in a protective film and Japanese Patent Laid-Open No. Sho 63-131103 describes the use of a mixture of a melamine resin and an epoxy resin as a main component in a protective film.
Epoxy resins have been shown to have desirable properties in terms of adhesive strength and resistance to heat, chemicals and water. For example, Japanese Patent Laid-Open No. Hei 08-050289 describes a curable resin composition including a glycidyl methacrylate polymer and a phenolic curing agent. Japanese Patent Laid Open No. Hei 08-201617 describes a resin composition including an epoxy resin, a curing agent, and an organic solvent, wherein the curing agent is the reaction product of a styrene-maleic anhydride copolymer and an amine.
Epoxy resins may react rapidly with curing agents. Thus, when epoxy resins are mixed with curing agents in so-called “two solution-type” or “two-pot” compositions, they are generally mixed immediately before use. In contrast, “one solution-type” or “one pot” compositions may be applied to a substrate in substantially the same form that they are stored in. Two solution-type compositions may be difficult to handle and may be unsuitable for industrial scale use due to the need for mixing and the relatively limited time frame for application after mixing However, epoxy resins have been generally known in the art to be unsuitable for use in one solution-type compositions.
Other two solution-type compositions have been modified to improve storage stability. For example, Japanese Patent Laid-Open No. 2001-091732 describes a technique for improving storage stability by protecting a polyfunctional carboxylic compound with a vinyl ether. However, the protection of the polyfunctional carboxylic acid may require a complicated procedure. Further, the vinyl ether may be harmful to humans, and so the industrial applicability of this procedure is uncertain.
Thus, it would be desirable to prepare one solution-type compositions that provide the desirable transparency, film strength, heat resistance, acid resistance and base resistance.